scholarly journals Quantum Crystallography in the Last Decade: Developments and Outlooks

Crystals ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 473 ◽  
Author(s):  
Alessandro Genoni ◽  
Piero Macchi
Keyword(s):  
Electron Density ◽  
Review Article ◽  
Quantum Mechanical ◽  
Spin Models ◽  
The Past ◽  
Core Electrons ◽  
Mechanical Information ◽  
Quantum Crystallography ◽  
Density Modelling

In this review article, we report on the recent progresses in the field of quantum crystallography that has witnessed a massive increase of production coupled with a broadening of the scope in the last decade. It is shown that the early thoughts about extracting quantum mechanical information from crystallographic experiments are becoming reality, although a century after prediction. While in the past the focus was mainly on electron density and related quantities, the attention is now shifting toward determination of wavefunction from experiments, which enables an exhaustive determination of the quantum mechanical functions and properties of a system. Nonetheless, methods based on electron density modelling have evolved and are nowadays able to reconstruct tiny polarizations of core electrons, coupling charge and spin models, or determining the quantum behaviour at extreme conditions. Far from being routine, these experimental and computational results should be regarded with special attention by scientists for the wealth of information on a system that they actually contain.

scholarly journals Determination of the electron density in methyl (±)-(1S,2S,3R)-2-methyl-1,3-diphenylcyclopropanecarboxylate using refinements with X-ray scattering factors from wavefunction calculations of the whole molecule

2013 ◽  
Vol 69 (8) ◽  
pp. 910-914 ◽  
Author(s):  
John Bacsa ◽  
John Briones
Keyword(s):  
Electron Density ◽  
Title Compound ◽  
Cyclopropane Ring ◽  
Topological Analysis ◽  
Quantum Mechanical ◽  
Quantum Mechanical Calculations ◽  
X Ray ◽  
Compound C ◽  
X Ray Scattering

The molecule of the title compound, C18H18O2, is a substituted cyclopropane ring. The electron density in this molecule has been determined by refining single-crystal X-ray data using scattering factors derived from quantum mechanical calculations. Topological analysis of the electron densities in the three cyclopropane C—C bonds was carried out. The results show the effects of this substitution on these C—C bonds.

scholarly journals An Experimental Study and Model Determination of the Mechanical Stiffness of Paper Folds

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Clémentine Pradier ◽  
Jérôme Cavoret ◽  
David Dureisseix ◽  
Claire Jean-Mistral ◽  
Fabrice Ville
Keyword(s):  
Identification Problems ◽  
Mechanical Stiffness ◽  
The Past ◽  
Folding Paper ◽  
Locality Principle ◽  
Mechanical Information ◽  
Model Determination ◽  
Experimental Values ◽  
Deterministic Behavior

Over the past few decades, folding paper has extended beyond the origami deployable applications to reach the engineering field. Nevertheless, mechanical information about paper behavior is still lacking, especially during folding/unfolding. This article proposes an approach to characterize the paper fold behavior in order to extract the material data that will be needed for the simulation of folding and to go a step further the single kinematics of origami mechanisms. The model developed herein from simple experiments for the fold behavior relies on a macroscopic local hinge with a nonlinear torsional spring. Though validated with only straight folds, the model is still applicable in the case of curved folds thanks to the locality principle of the mechanical behavior. The influence of both the folding angle and the fold length is extracted automatically from a set of experimental values exhibiting a deterministic behavior and a variability due to the folding process. The goal is also to propose a methodology that may extend the simple case of the paper crease, or even the case of thin material sheets, and may be adapted to other identification problems.

Transmission Electron Microscopy of Protein Macromolecules

1971 ◽  
Vol 29 ◽  
pp. 424-425
Author(s):  
Henry S. Slayter
Keyword(s):  
Biological Systems ◽  
Metal Vapor ◽  
Resolving Power ◽  
Electron Microscopic ◽  
Chemical Methods ◽  
Molecular Weights ◽  
The Past ◽  
Physical Chemical ◽  
Transmission Electron

Electron microscopic methods have been applied increasingly during the past fifteen years, to problems in structural molecular biology. Used in conjunction with physical chemical methods and/or Fourier methods of analysis, they constitute powerful tools for determining sizes, shapes and modes of aggregation of biopolymers with molecular weights greater than 50, 000. However, the application of the e.m. to the determination of very fine structure approaching the limit of instrumental resolving power in biological systems has not been productive, due to various difficulties such as the destructive effects of dehydration, damage to the specimen by the electron beam, and lack of adequate and specific contrast. One of the most satisfactory methods for contrasting individual macromolecules involves the deposition of heavy metal vapor upon the specimen. We have investigated this process, and present here what we believe to be the more important considerations for optimizing it. Results of the application of these methods to several biological systems including muscle proteins, fibrinogen, ribosomes and chromatin will be discussed.

Literacy and Education: Fifth Release From the 1961 Census of Pakistan (Review Article)

1963 ◽  
Vol 3 (3) ◽  
pp. 424-442
Author(s):  
Jamila Akhtar
Keyword(s):  
Population Growth ◽  
Urban Areas ◽  
Review Article ◽  
Interim Report ◽  
Educational Levels ◽  
Rural And Urban Areas ◽  
The Past ◽  
Review Articles ◽  
Rural And Urban ◽  
Age And Sex

This review of the Literacy and Education Bklletin1 of the 1961 Census is fourth in the series of review articles published in this journal2. The Bulletin under review forms a part of the interim report on the characteristics of the population of Pakistan. It gives information on the number of illiterate and literate persons by age and sex for rural and urban areas on division and district basis; illiterate and literate.population in selected cities and towns; and the educational levels attained by the literate population by age and sex for divisions and districts. Relevant statistical notes and statements precede the tables in the Bulletin. The objective of this review is to describe the meaningfulness and significance of literacy statistics. To this end, a distinction is made between formal and functional levels of literacy. Comparisons of the 1951 and 1961 census figures are undertaken to indicate the progress of literacy and education during the past decade with reference to the effect of intercensal rate of population growth on such progress. Certain questions regarding the reliability of data are raised, which emphasize the need for caution in the interpretation of literacy statistics.

Nucleosides and Nucleoside Analogues as Emerging Antiviral Drugs

2020 ◽  
Vol 17 ◽  
Author(s):  
Mohamed Ibrahim Elzagheid
Keyword(s):  
Significant Role ◽  
Mode Of Action ◽  
Crucial Role ◽  
Viral Infections ◽  
Antiviral Drugs ◽  
Review Article ◽  
Nucleoside Analogues ◽  
The Past ◽  
Nucleoside Drugs

: Nucleosides and their analogues have been in use for many years and have become essential for treating patients with viral infections. Many additional nucleoside drugs have been approved over the past decades. This strongly demonstrates how important these compounds are and the crucial role they play. Given that a significant amount of research and literature has been documented regarding nucleoside analogues, this review article mainly focuses the discussion on nucleosides and nucleoside analogous that have proven to play significant role or be emerging in the treatment of known viral infections. This covers the names, structures, applications, toxicity, and mode of action of relevant nucleoside analogues.

Formation of Carbon-Oxygen Bond Mediated by Hypervalent Iodine Reagents Under Metal-free Conditions

2020 ◽  
Vol 17 ◽  
Author(s):  
Ayesha Jalil ◽  
Yaxin O Yang ◽  
Zhendong Chen ◽  
Rongxuan Jia ◽  
Tianhao Bi ◽  
...  
Keyword(s):  
Natural Products ◽  
Bond Formation ◽  
Building Blocks ◽  
Review Article ◽  
Hypervalent Iodine ◽  
Metal Free ◽  
Bioactive Natural Products ◽  
The Past ◽  
Oxygen Bond ◽  
Privileged Scaffolds

: Hypervalent iodine reagents are a class of non-metallic oxidants have been widely used in the construction of several sorts of bond formations. This surging interest in hypervalent iodine reagents is essentially due to their very useful oxidizing properties, combined with their benign environmental character and commercial availability from the past few decades ago. Furthermore, these hypervalent iodine reagents have been used in the construction of many significant building blocks and privileged scaffolds of bioactive natural products. The purpose of writing this review article is to explore all the transformations in which carbon-oxygen bond formation occurred by using hypervalent iodine reagents under metal-free conditions

Crime and Punishment

2017 ◽  
Author(s):  
Richard Adelstein
Keyword(s):  
Criminal Liability ◽  
Court Case ◽  
Efficient Allocation ◽  
Two Stage ◽  
Crime And Punishment ◽  
The Past ◽  
Ex Post ◽  
Ex Ante ◽  
Supreme Court Case

This chapter elaborates the operation of criminal liability by closely considering efficient crimes and the law’s stance toward them, shows how its commitment to proportional punishment prevents the probability scaling that systemically efficient allocation requires, and discusses the procedures that determine the actual liability prices imposed on offenders. Efficient crimes are effectively encouraged by proportional punishment, and their nature and implications are examined. But proportional punishment precludes probability scaling, and induces far more than the systemically efficient number of crimes. Liability prices that match the specific costs imposed by the offender at bar are sought through a two-stage procedure of legislative determination of punishment ranges ex ante and judicial determination of exact prices ex post, which creates a dilemma: whether to price crimes accurately in the past or deter them accurately in the future. An illustrative Supreme Court case bringing all these themes together is discussed in conclusion.

Sampling, Preservation and Counting of Samples II: Zooplankton

2017 ◽  
Author(s):  
Peter H. Wiebe ◽  
Ann Bucklin ◽  
Mark Benfield
Keyword(s):  
Genetic Analysis ◽  
High Speed ◽  
Morphological Analysis ◽  
Taxonomic Composition ◽  
Sampling Techniques ◽  
Sample Analysis ◽  
Sample Preservation ◽  
The Past ◽  
Plankton Collection

This chapter reviews traditional and new zooplankton sampling techniques, sample preservation, and sample analysis, and provides the sources where in-depth discussion of these topics is addressed. The net systems that have been developed over the past 100+ years, many of which are still in use today, can be categorized into eight groups: non-opening/closing nets, simple opening/closing nets, high-speed samplers, neuston samplers, planktobenthos plankton nets, closing cod-end samplers, multiple net systems, and moored plankton collection systems. Methods of sample preservation include preservation for sample enumeration and taxonomic morphological analysis, and preservation of samples for genetic analysis. Methods of analysis of zooplankton samples include determination of biomass, taxonomic composition, and size by traditional methods; and genetic analysis of zooplankton samples.

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